Quantitative analysis of (l)-ephedrine and (d)-pseudoephedrine in plasma by high-performance liquid chromatography with fluorescence detection.

Quantitative analysis of (l)-ephedrine (l-Ep) and (d)-pseudoephedrine (d-Ps) in plasma by high-performance liquid chromatography (HPLC) is described. The newly developed method is based on a precolumn derivatization with 5-dimethyl-aminonaphthalene-1-sulfonyl chloride (DNSC1) in acetonitrile. The diastereomers formed were separated on a reversed phase column by HPLC with fluorescence detection employing 0.6% phosphate buffer (pH 6.5)-methanol (3:8, v/v) as mobile phase. The detection limit of each Ephedra alkaloid stereoisomer was 0.5 ng at a signal-to-noise ratio of 3:1, the linear response to each stereoisomer being 1-800 ng.ml-1. The plasma level profile of l-Ep and d-Ps in guinea pig was investigated by this method. The determination of l-Ep and d-Ps in plasma of a volunteer after oral administration of Xiao Qinglong Heji was also performed.